Enhanced photo-ozonation for on-board marine oily wastewater treatment: An integrated study on efficiency and microbial trajectory

On-board treatment of marine oily wastewater can avoid the costly transportation of large waste streams to shorelines. Employing on-board photo-ozonation, particularly ultraviolet (UV) plus ozone (O₃) (UVO₃) and persulfate (PS) enhanced UVO₃ (UVO₃PS), can realize promisingly rapid degradation of various oil components. However, direct discharge of treated effluents to marine environments would still bring unpredictable impacts on ecosystems. Herein, we integrate a photo-ozonation system with marine microcosms to clearly elucidate the treatment efficiency and microbial trajectory responding to the treated light and heavy oily wastewater over time. Results show that both processes can mineralize above 90% of crude oil within 60 minutes by substantially removing n-alkanes and aromatics, and the incorporation of PS generates more powerful radicals to enhance the breakdown of products with nearly 36% lower operating cost. The microcosm results evidence that diverse hydrocarbon-degrading bacteria are enriched over time. Besides, the long-term incubation of UVO₃PS-treated oily wastewater enriches members capable of degrading labile organics, intensifies the co-occurrence of genera participating in nitrogen and sulfur metabolisms, and stimulates the microbial trajectory for natural attenuation. Due to the environmental and economic benefits provided by UVO₃PS, it is believed that this process can be selected as a promising option for on-board marine oily wastewater treatment.